1. Field of the Invention
The present invention relates to a radio frequency (hereinafter, referred to simply as RF) transmitting device of a mobile radio communication base station system in a code division multiple access system (hereinafter, referred to simply as CDMA) and more particularly, to an RF transmitting device of a mobile radio communication base station system in a CDMA system which is capable of digital-modulating baseband signals which are converted into band spread signals by using the same path which three frequency assignment frequency signals have for an RF in a multi-carrier mobile radio communication system supporting three frequency assignment, digital-coupling the modulated signals, and up-converting the digital-coupled signal into an intermediate frequency signal and an RF signal in a sequential order, thereby transmitting the up-converted signal.
2. Discussion of Related Art
A general mobile radio communication base station system in a CDMA system includes a switching system and a cell equipment. Of course, the above system contains a large number of functional devices which are all embodied with various kinds of equipments.
The key part of the mobile radio communication base station system is composed of a channel card, a sector interface card, an analog common card and a digital shelf on which a terminal card is packaged. Additionally, it contains a tranceiver shelf which up-converts an IF signal outputted from the digital shelf in an ultra high frequency (UHF) signal and reversely, down-converts the UHF signal into the IF signal. In the tranceiver shelf the sector interface card is installed to couple baseband forward signals received from the channel cards and up-convert the coupled signal into the IF signal. The sector interface card receives the coupled baseband transmitting signals coupled from the analog common cards and couples and amplifies the received signals. The coupled signal is coupled, through a low-pass filter (LPF), to the IF signal, i.e., the delayed signal by the phase of 0° and 90° of 4.95 MHz and transmitted as the IF signal of 4.95 MHz, through a band-pass filter (BPF), to an RF rack. Therefore, the RF rack converts the received IF signal of 4.95 MHz into the UHF signal, for transmitting the converted signal through an antenna.
Referring to FIGS. 1 and 2, now, an explanation of the construction and operation of the general mobile radio communication base station system will be discussed.
FIG. 1 is a block diagram illustrating the construction of a general mobile radio communication base station system. In construction, referring to FIG. 2, the system comprises: a base station control processor (BCP) 2 which operates and controls one base station; a base station interconnection network (BIN) 3 which serves as a packet router between the base station and a control station 1 via a line E1 or T1 and interfaces high-level data link control (HDLC) packet data between the processors within the base station; a time and frequency unit (TFU) 4 which generates a reference frequency and a timing synchronizing signal to thereby execute the synchronization for each processor within the base station and the timing synchronization with an adjacent base station; a digital unit (DU) 5 composed of a first digital unit 5a and a second digital unit 5b, which modulates/demodulates the data signal and voice signal transmitted/received through a CDMA channel; and an RF unit (RFU) 6 composed of a first RF unit 6a and a second RF unit 6b, which converts an UHF signal received from a mobile station into an IF signal to thereby transmit the converted IF signal to the digital unit 5, receives the IF signal inputted from the digital unit 5 to thereby convert the received IF signal into the UHF signal, and amplifies the converted UHF signal to a predetermined level to thereby execute space-radiation for the amplified UHF signal. The RF unit 6 is divided into an RF receiving device and an RF transmitting device.
FIG. 2 is a block diagram illustrating a prior art RF transmitting device of a digital mobile radio communication base station system in a CDMA system.
As shown, the conventional RF transmitting device comprises: three channel cards 11, 12 and 13 which output digital baseband signals for supporting three frequency assignment to I/Q (in-phase/quadrature) channels by each frequency assignment; three analog processors 20, 30 and 40 which are correspondingly connected to the channel cards 11, 12 and 13, convert the baseband signals on the I/Q channels by each frequency assignment into analog signals, and execute a quadrature phase shifting keying (QPSK) modulation for each of the converted analog baseband signals to thereby output the modulated signal; three analog up-converters 50, 60 and 70 which are correspondingly connected to the three analog processors 20, 30 and 40, convert the modulated signals by each frequency assignment outputted from the three analog processors 20, 30 and 40 into IF signals, and convert the converted IF signals into transmitting frequency (RF) signals to thereby output the converted RF signals; a transmitting signal coupler 80 which couples the RF signals by the frequency assignment outputted from the three analog up-converters 50, 60 and 70 and outputs the coupled signal on a single path, and a transmitting unit 90 which amplifies the RF signal outputted from the transmitting signal coupler 80 to a predetermined level, limits the frequency band of the RF signal to prevent the affect on the frequency used in another communication system and transmits the band-limited RF signal via an antenna. In this case, the baseband signals, which are outputted from the three channel cards 11, 12 and 13, that is, the channel cards by the frequency assignment are 0FA-I, 0FA-Q, 1FA-I, 1FA-Q, 2FA-I and 2FA-Q.
The three analog processors 20, 30 and 40 by the frequency assignment 0FA, 1FA and 2FA include D/A converters 21, 31 and 41 for converting the baseband signals outputted from the channel cards 11, 12 and 13 into the analog signals and analog modulators 22, 32 and 42 for executing the QPSK modulation for the analog baseband signals outputted from the D/A converters 21, 31 and 41 to thereby up-convert the modulated signal into a frequency signal of 4.95 MHz. Each of the three analog up-converters 50, 60 and 70 by the frequency assignment contains local oscillators and mixers (which are not shown in the drawing). And, the three analog up-converters 50, 60 and 70 by the frequency assignment comprise: first frequency up-converters 51, 61 and 71 for up-converting the frequency signals of 4.95 MHz outputted from the analog modulators 22, 32 and 42 into the IF signals by using the corresponding local oscillator and mixer; channel filters 52, 62 and 72 for filtering the IF signals outputted from the first frequency up-converters 51, 61 and 71 with a frequency bandwidth of 1.25 MHz to thereby output the filtered signals; and second frequency up-converters 53, 63 and 73 for up-converting the filtered signals in the channel filters 52, 62 and 72 into the RF signal by using the corresponding local oscillator and mixer. In this case, the local oscillator in each of the second frequency up-converters 53, 63 and 73 is, preferably, a variable local oscillator for channel division.
Under the above construction, an explanation of the operation of the conventional RF transmitting device will be discussed.
First, the channel cards 11, 12 and 13 by each frequency assignment output the CDMA digital signals to the D/A converters 21, 31 and 41 of the analog processors 20, 30 and 40 through the I/Q channels by each frequency assignment 0FA-I, 0FA-Q, 1FA-I, 1FA-Q, 2FA-I and 2FA-Q. At this time, the output signals are the baseband signals. The baseband signals on the I/Q channels outputted from the channel cards 11, 12 and 13 are converted into the analog signal by means of the D/A converters 21, 31 and 41 and then outputted to the analog modulators 22, 32 and 42. The QPSK modulation on the I/Q channels for the analog baseband signals outputted from the D/A converters 21, 31 and 41 is executed in the analog modulators 22, 32 and 42, respectively. Then, the signals on the I/Q channels by each frequency assignment are coupled and transmitted to the first frequency up-converters 51, 61 and 71 of the analog frequency up-converters 50, 60 and 70. At this time, the baseband signals are up-converted into the frequency signal of 4.95 MHz. The first frequency up-converters 51, 61 and 71 of the analog frequency up-converters 50, 60 and 70 convert the signals which are made by coupling the signals on the I/Q channels into the IF signal by using the local oscillator and mixer and transmit the converted IF signals to the channel filters 52, 62 and 72. In other words, the coupled signal on the I/Q channels and the local frequency generated from the local oscillator are mixed by means of the mixer and then converted into the IF signal. The converted IF signals, from which the signals being out of the frequency band by each frequency assignment are filtered by means of the channel filters 52, 62 and 72 to thereby protect the transmitting signals thereof, are outputted to the second frequency up-converters 53, 63 and 73. At this time, the channel filters 52, 62 and 72 are, preferably, a surface acoustic wave (SAW) filter having the bandwidth of 1.25 MHz. Next, the second frequency up-converters 53, 63 and 73 convert the IF signals outputted from the channel filters 52, 62 and 72 into the RF signals by using the local oscillator and output the converted RF signals by the frequency assignment to the transmitting signal coupler 80. At this time, the local oscillator, which is used in the second frequency up-converters 53, 63 and 73, respectively, is a variable local oscillator for channel division. Therefore, the signal of each local oscillator is generated at the frequency intervals of each frequency assignment. The three frequency assignment signals, which have been converted into the RF signals, are coupled in the transmitting signal coupler 80 and outputted to the transmitting unit 90. Finally, the transmitting unit 90 amplifies the coupled RF signal outputted from the transmitting signal coupler 80 to the predetermined level via a low-power amplifier (which is omitted in the drawing), limits the frequency band of the RF signal to prevent the affect on the frequency used in another communication system and transmits the RF signal via the antenna.
However, the conventional RF transmitting device of the mobile radio communication base station system in the CDMA system suffers from problems that the production cost increases, because the hardware for converting the baseband signal into the RF signal is constructed separately by each frequency assignment, that the size of system is bulky, because the construction is complicated, and that the stability of system to temperature and time becomes deteriorated, because the process for up-converting the baseband signal into the IF signal is carried out in an analog manner. Additionally, the conventional RF transmitting device suffers from problems that it is difficult to extend the frequency assignment, the hardware configuration is complicated, and that the expense increases, because the frequency up-converting process is carried out by each frequency assignment and the extension of the frequency assignment is made each frequency assignment.